JS实现的哈夫曼编码示例【原始版与修改版】

本文实例讲述了js实现的哈夫曼编码。分享给大家供大家参考，具体如下：

原始版

function cal(str) {
  if (typeof str !== 'string' || str.length < 1) {
    return;
  }
  var map = {};
  var i = 0;
  while(str[i]) {
    map[str[i]] ? map[str[i]]++ : (map[str[i]] = 1);
    i++;
  }
  return map;
}
function sort(map) {
  map = map || {};
  var result = [];
  for (key in map) {
    if(map.hasownproperty(key)) {
      var obj = {
        key: key,
        val: map[key]
      };
      result.push(new node(null, null, obj));
    }
  }
  return result.sort(function(x,y){return x.data.val > y.data.val});
}
function node(left, right, data) {
  this.left = left;
  this.right = right;
  this.data = data;
}
function maketree(table) {
  var i = 0;
  var len = table.length;
  var node1;
  var node2;
  var parentnode;
  while(table.length > 1) {
    parentnode = new node(table[i], table[i+1], {key: null, val: table[i]['data'].val + table[i+1]['data'].val});
    table.splice(i,2);
    table.unshift(parentnode);
    table.sort(function(x,y){return x.data.val > y.data.val});
  }
  return table;
}
function encode(str, ret) {
  if (typeof str !== 'string' || str.length < 1) {
    return;
  }
  var i = 0;
  var result = '';
  while(str[i]) {
    result += ret[str[i++]];
  }
  return result
}
function reverseret(ret) {
  var result = {};
  for (key in ret) {
    if(ret.hasownproperty(key)) {
      result[ret[key]] = key;
    }
  }
  return result;
}
function decode(str, ret) {
  var i = 0;
  var result = '';
  var data = '';
  var map = reverseret(ret);
  while(str) {
    result += str[i++];
    if (result in map) {
      data += map[result];
      str = str.replace(new regexp("^"+result),'');
      result = '';
      i = 0;
    }
  }
  console.log(data)
}
function traversal(tree, code, ret) {
  if (tree.left !== null) {
    traversal(tree.left, code + '0', ret);
  } else {
    ret[tree.data.key] = code;
  }
  if (tree.right !== null) {
    traversal(tree.right,code + '1', ret);
  } else {
    ret[tree.data.key] = code;
  }
}
var ret = {};
var str = 'ew qew qd ef 24 gf ewr getelementsbytagname';
traversal(maketree(sort(cal(str)))[0],'', ret)
decode(encode(str, ret), ret)
btoa(encode(str,ret))

修改版

function huffman(str) {
  // 需要编码的字符串
  this.str = str;
  // 键和频率映射表
  this.keycountmap = null;
  // 编码和键的映射表
  this.codekeymap = {};
  // 键和编码的映射表
  this.keycodemap = {};
  // 哈夫曼树节点列表
  this.nodelist = null;
  // 哈夫曼树根节点
  this.root = null;
  // 哈夫曼编码后的01序列
  this.code = null;
}
huffman.prototype.cal = function cal() {
  str = this.str;
  var map = {};
  var i = 0;
  while(str[i]) {
    map[str[i]] ? map[str[i]]++ : (map[str[i]] = 1);
    i++;
  }
  this.keycountmap = map;
}
huffman.prototype.sort = function sort() {
  map = this.keycountmap;
  var result = [];
  for (key in map) {
    if(map.hasownproperty(key)) {
      var obj = {
        key: key,
        val: map[key]
      };
      result.push(new node(null, null, obj));
    }
  }
  this.nodelist = result.sort(function(x,y){return x.data.val > y.data.val});
}
function node(left, right, data) {
  this.left = left;
  this.right = right;
  this.data = data;
}
huffman.prototype.maketree = function maketree() {
  var i = 0;
  var len = this.nodelist.length;
  var node1;
  var node2;
  var parentnode;
  var table = this.nodelist;
  while(table.length > 1) {
    parentnode = new node(table[i], table[i+1], {key: null, val: table[i]['data'].val + table[i+1]['data'].val});
    table.splice(i,2);
    table.unshift(parentnode);
    table.sort(function(x,y){return x.data.val > y.data.val});
  }
  this.root = table[0] || new node();
  return this.root;
}
huffman.prototype.traversal = function traversal(tree, code) {
  if (tree.left !== null) {
    traversal.call(this,tree.left, code + '0');
  } else {
    this.keycodemap[tree.data.key] = code;
  }
  if (tree.right !== null) {
    traversal.call(this, tree.right,code + '1');
  } else {
    this.keycodemap[tree.data.key] = code;
  }
}
huffman.prototype.encode = function encode() {
  this.cal();
  this.sort();
  var root = this.maketree();
  this.traversal(root, '');
  var ret = this.keycodemap;
  var i = 0;
  var result = '';
  var str = this.str;
  while(str[i]) {
    result += ret[str[i++]];
  }
  this.code = result;
  console.log('encode:' + result);
  return result
}
huffman.prototype.reversemap = function reversemap() {
  var ret = this.keycodemap;
  var result = {};
  for (key in ret) {
    if(ret.hasownproperty(key)) {
      result[ret[key]] = key;
    }
  }
  this.codekeymap = result;
  return result;
}
huffman.prototype.decode = function decode() {
  var i = 0;
  var result = '';
  var data = '';
  var map = this.reversemap();
  var str = this.code;
  while(str) {
    result += str[i++];
    if (result in map) {
      data += map[result];
      str = str.replace(new regexp("^"+result),'');
      result = '';
      i = 0;
    }
  }
  console.log("decode:" + data)
}
huffman.prototype.encodebase64 = function() {
  try {
    var base64 = btoa(this.code);
    return base64;
  } catch(e) {
    return '';
  }
}
var str = 'ew qew qd ef 24 gf ewr getelementsbytagname';
var huffman = new huffman(str)
huffman.encode(str)
huffman.decode();
huffman.encodebase64();

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